The secrets of bass trap placement

One of the things I get asked quite often is ‘where is the best place to put bass traps and why?’. This short article will explain a little about what bass traps do and how they work before going on to discuss the three different places where bass traps can be placed.

Bass Traps and room modes

The most effective place to add bass traps is in the corners of the room since all room modes have a pressure high or node in the corner. The three key points about room modes are summarized below, but if you want to know more be sure to read the detailed article Room Modes and Room Mode Calculators on our main website.

Bass traps are acoustic absorbers designed specifically to be effective down into the frequency range where room modes cause problems. Typical 3″ thick fiberglass absorber panels start to lose effectiveness at around 250Hz whereas most of our modal resonance problems occur below 150Hz in the so called ‘sparsely populated modal region’. Bass traps typically incorporate elements such as membranes, airspaces and additional thicknesses of fiberglass (up to 6″ or more) to extend absorption down into the double digit range.

The three places where Bass Traps can be installed

There are three main places where bass traps can be installed:

Tri-corner bass trap

1. Tri-corner, where the two walls meet the ceiling or the floor.

There are 8 tri-corners in a square or rectangular room, although placing bass traps at the four on the floor may not be practical. Placing a bass trap in this location affects all room modes. There are specific triangular bass traps designed for installation in the tri-corners, such as the Primacoustic Cumulus.

Corner mount bass trap

2. A wall / wall corner, such as the interface of the side and back wall. There are 4 corners in a square or rectangular room. Placing a bass trap in a wall / wall corner will affect the main length and width modes and some of the height modes. Stacking two 4′ tall corner mount bass traps such as the Primacoustic MaxTrap, one above the other, in the corner can affect all room modes, since the tri-corner location will also be covered in a standard 8ft ceilinged house.

Wall mount bass trap

3. A wall or ceiling. There is plenty of wall and ceiling area available in most rooms for installing bass traps such as the Primacoustic FullTrap or the amazing RPG Modex Plate. Generally a wall mount bass trap will most strongly impact the room modes caused by the two parallel surfaces. Placing a bass trap on the side wall, for example, will mainly affect the width mode.

Are there any other things you want to know about bass trap placement or bass traps in general?

46 thoughts on “The secrets of bass trap placement”

Hi, I have a room of 3m x 3m x 3. A perfect cube. I have a closet covering a side wall almost completly. So the available space is 3x2x3. I have a lot of cancelation and boming in bass. Im wondering where would be the best places to put the bass traps. 2 of the corners are not available for placing as there is a door and also the closet. Any sugestions would be apreciatedThanks

Hi Fernando, thanks for asking this great question! That is going to be a very hard room to fix because all the room modes are going to coincide creating a significant peak in the frequency response and extended ringing in the time domain. It is the extended ringing that is the main cause of the boominess you are observing.

One place I always like to put acoustic treatment is on the ceiling. You can use the wall / ceiling corner and the wall / wall / ceiling corner for starters. After that I would recommend adding bass trapping to the ceiling. As much as you can really!

Hi, I have a room that is 17.5 feet wide, 13 feet deep, 8 feet tall, with draped glass windows on the right side, and open on the left side, and carpet. The walls are concrete, and the ceiling is concrete with acoustic coating. The speakers are located on the front wall (17.5 feet wide) and the listening position is near the back wall. I have serious bass problems, particularly at around 60hz and 100hz.

I installed 4 foam bass traps on each of the wall/ceiling corners of the front and back walls, and 16 foam studio tiles on the each of the front and back walls as well. Is there anything else I do or better locations for bass traps that would help get this under control?

First of all thanks for leaving a comment! It's always reassuring to know that people are really interested in getting good sound and are aware of the impact room acoustics has on this.

There are a couple of problems with your setup:1) a room with concrete walls and ceiling is going to have problems with room modes since the room is not providing any supporting low frequency absorption. A sheetrock (called gypsum board or plasterboard in other areas of the world) / wooden stud construction actually flexes and is a reasonably good absorber of low frequency energy. So bass trapping, and likely tuned absorbers, are going to be required in your space to bring the low frequency decay under control2) a listening position against or very close to a wall puts that seat in an area where all room modes have a pressure node (these correspond to peaks in the frequency response since they are where energy builds up)3) foam bass traps absorbers are what is called a broadband bass absorber and typically only absorb down to maybe 150Hz or even only 200Hz with any real effect. The foam tiles will not do anything for bass absorption. A useful measurement that shows absorption over the frequency spectrum is the absorption coefficient. A coefficient of 1 indicates that all incident energy is absorbed in that frequency range. In our opinion all manufacturers of acoustical products should produce a table showing absorption coefficient since it very clearly shows where a product is effective and where it is not.

A good place to start would be to use a room mode calculator – input your room dimensions and see if the peaks you are observing correspond to room modes. I am very sure that they will be. Once you've confirmed this then you can decide what bass trapping is required to combat the issues at those frequencies. For your space in particular you will need to seriously upgrade your bass trapping. Products like the Primacoustic MaxTrap are effective down to about 70Hz. Below that you need to use custom built bass traps or the RPG Modex Plate. Acoustic Frontiers can help with both products – just get in touch!

The other important thing to know is that positioning of both loudspeaker and listener (but particularly listener is an effective tactic to deal with resonances). If you can find a null for the mode in question then you can put your listening seat in that location. Just beware that you might have put yourself in the peak for another mode by moving your seat though! Nulls can be found either by playing a sine wave tone at that frequency and walking around the room to find the peaks (where the sound is louder) and nulls (where the sound disappears) or by using an acoustic measurement product such as XTZ Room Analyzer.

The best combination is normally to add bass trapping and to seek a position for the listening seat where the frequency response is most even. A third option is to use subwoofers in a mode cancelling arrangement.

I'm not sure I understand how the room mode calculator is displaying the frequencies, since it displays 28 values and I'm not sure if these all apply to all axes, however several of these are in the ranges that I have noticeable trouble with as evidenced by the SPL meter with test tones. In particular though, I notice that the ~60hz peak is the one that is most physically uncomfortable to listen to.

I am discovering too late that I bought the wrong type of bass traps for the frequencies that are most problematic, but given your recommendation of other bass traps, I am left wondering where I would install them. The problem is that my room does not really have vertical corners where traps can be installed as seems to be the standard recommendation. Can I expect the same benefits with these bass traps installed on the back wall or on the horizontal corners between the front/back walls and ceiling where the foam is currently placed?

I have experimented with moving the speakers and listening position as much as practicality allows, although I have noticed what you describe which is that the problem frequency merely shifts, and to alleviate the uncomfortable deep bass pressure, the speakers have to be 5-6 feet into the 13 foot deep room. I am interested to read more about the mode cancelling subwoofer arrangement that you describe.

The RealTraps calculator shows the length, width and height modes separately. Even better is to find one of the room mode spreadsheets floating around on the internet which show all of the modes and their order.

The best placement of bass traps does depend on which surfaces are causing the problematic standing waves to form. You want to place the bass traps in a location where they in the pressure peaks for those standing waves. For example if you can associate your problem around 60Hz with, say, the 2nd length mode of the room, then you know the best place to put bass traps to deal with that standing wave will be anywhere on the front and back walls.

Its worth knowing that Acoustic Frontiers does offer free consultations to help out with just this kind of problem. And of course our main reason for being in business is to professionally solve exactly these type of issues.

The mode cancelling subwoofer arrangement is very effective but also requires that you know which surfaces are causing the problematic standing waves. You place one subwoofer in a peak for the mode and the other in a null, and voila, the room mode ceases to exist! See this short article for more information.

I will definitely try out a free consultation before spending any more money on the wrong products, or installing in the wrong positions. Expert advice is of tremendous value. Since I currently have three non-identical subwoofers to experiment with, I'll also be trying the cancellation approach. Does this require that one of the subs be used with inverted polarity, or is this achieved by placement alone? The other thing that comes to mind, is whether it may be possible to use a single subwoofer on an opposing wall from the speakers that are creating the bass boominess. That is to say, rather than multiple subs, can a single sub cancel out the modes created by large full range speakers? It is great to know there are some options available and this site has proven to be a great resource.

The subs are run with normal polarity – it is putting them in opposite 'poles' of the standing wave that creates the mode cancelling effects.

It may be possible to use a single sub opposite say a full range speaker as long as there is significant acoustic overlap in the region of the mode in question AND the placement puts the speakers and sub in opposite poles for the standing wave. For example, if the mode you want to cancel is at 70Hz then you need both speakers and sub to be playing at pretty much the same level at that frequency. Normally if you use a crossover between sub and mains then this will not be the case since the output of one is rolled off in the pass band of the other. Furthermore the placement of the mains is typically in a location where soundstaging and imaging is the best, and this placement is rarely going to coincide with a pole for the mode you are attempting to cancel…

Thanks Will for your comment… are you referring to the aluminium foil on FRK type slabs?

Any type of membrane will have the effect of transforming sound pressure into movement. That movement is then damped by the fiberglass or glasswool core, which turns it into heat. This is particularly useful since most of the time we put our bass traps in areas of high pressure but low sound velocity (i.e. near the walls) so membrane based traps help to increase absorption by working with the physics of the situation.

Where in the UK are you based? I spent 8 years in London before moving over to California. Can't say I miss the weather one little bit!

We are building our own bass traps and acoustical panels at our church. We seem to have problems with low frequencies. Our back wall is 50' wide with a cathedral acoustical tile ceiling. I'm wondering about placement for our bass traps? I know that the corners are a better place for them. But, that back wall is very big and flat. The distance from the stage to the back wall is roughly 45'. Do we also add bass traps in the field of that wall? Do I make all bass traps 6"?

Have you done any acoustical measurements of your church? It might be worth doing some before building a lot of bass traps to understand what the issues are in your space. There are low cost options for acoustical measurement including XTZ Room Analyzer II Pro and my remote Acoustical Diagnosis Service. Generally big rooms such as the one you describe don't have problematic issues in the low frequencies – the issues are more related to sounds taking a long time to decay in the lower midrange and midrange frequencies causing issues with speech intelligibility in particular.

In answer to your question the best place for bass traps depends on exactly what room modes you are trying to address. But your proposed location on the back wall and thickness would seem like a good start. Generally the thicker the better and if you can put some kind of hard membrane like hardboard or thick plastic over the top of fiberglass/rockwool then that also increases low frequency absorption at the cost of reduced midrange and high frequency absorption.

Hi great stuff here!I was just wondering; i have a 16' wide 32' long with 12' ceilings that gradually slope up to about 13' in the back. but it is only the full length on one side. about 20' on the left side wall 32.5 on the right. and this happens about the middle or the room width wise

i have 2 6inch thick 2×4 panels on the floor tri corners (front wall behind mixer and speakers) (O/C 703 rigid fibreglass)) and a 1st reflection panel on either side wall 2x4x 3inch thick (703) my question is if i were to make 2 more 6 inch bass panels would putting them in the 4 tricorners be better than standing them on top of aech other leaving the top corners untreated? also do i need a cloud with 12' ceiling? sorry also have panels behind the speakers .Thx a bunch(speakers are 3' out from wall)Darin

I was planning to buy the Cumulus bass traps for a 7 X 7 Whisper Room. Asking some of my peers what their thoughts on this were, I got the following response:

I would think a traditional 24 x48 corner bass trap would be a lot more effective than those Cumulus ones simply because they're so much bigger… mass is what absorbs bass. According to the specs page, the Cumulus panels don't deal with anything below 100Hz… I wouldn't think they'd be much help in a Whisper Room.

I am not familiar with Whisper Rooms but from a quick google it appears they are for voiceover recording? In which case it's unlikely that you would need bass absorption below 80Hz, since that's as low a frequency as vocals go. And most of the energy is actually in the 150Hz to 400Hz range. So products like the Primacoustic Cumulus will be fine for your needs.

Mass makes the difference for sound transmission but is not important for sound absorption e.g. you could have a very heavy piece of wood that would do nothing for sound absorption.

A lot of fantastic info on here , just wanted to say thanks to All involved …

Just a quick one

I have recently treated my home studio with Multiple acoustic foaming pads….,

I'd say that I've done almost 80% of the surrounding walls and ceilling with the pads I recently bought .. The actual pads I have used are either 60mil deep or 40mil deep, I'd say its about a 50/50 split…

Remaining I have 6 foam acoustic bass traps…. I was thinking to double stack the Bass Traps in the two corners behind my speakers with 4 traps , 2 in each corner with 1 on top of the other… And have the remaining 2 traps for the the two corners behind me (1 in each corner)

Question is , would you go with this spilt of Bass Traps or can you recommend a different approach … I'm also guessing the Wall / Celling Corners are more important than the Wall/Floor Corners therefore raising the traps would be better than having them on the floor

I wanted to buy the Owens Corning 703 rigid fiberglass as I heard it would work as long as it is 6' deep and a good amount off of the wall. How far should it be off the wall to really get those low frequencies below 120 and such? And also, the fiberglass is very expensive. I have about a 10' by 12' cube room…Could you also recommend anything more affordable to treat the whole room?

Incorporating some form of membrane into the absorber helps improve low frequency absorption significantly. Mass loaded vinyl, aluminum foil, kraft paper and cardboard are just some of the things that you can use as membranes.

You may not know it but in addition to selling off the shelf products from Primacoustic and RPG we also create custom designs for people just like yourself who want to DIY. Before any design is done, however, we need to analyze your room to identify the problematic areas and create a treatment strategy that works as a whole. See our acoustical diagnosis service for more information on this.

Be careful not to treat the whole room with absorbers, otherwise you will have a very dead space, almost like an anechoic chamber!

The right number of bass traps is the right number needed to solve the acoustical issues in your room! The only way to know therefore is to measure your room acoustics using a package such as XTZ Room Analyzer II Pro to understand how flat your frequency response is and what issues exist in terms of slow decay of sound due to room resonances. Target for a stereo system should be to keep 20-250Hz frequency response within a 10dB window. If you can get it tighter, then that’s great!

There is nothing wrong with putting bass traps in all four corners (and walls, wall/ceiling corners, etc) if you need them!

I have built ceiling to floor corner bass traps in my listening room and have a question. In the comments above you mentioned putting hard board over the fiberglass to increase low end. Can you explain, when you say on top, this would be the front of the bass trap? Thanks so much

If you add a membrane then you increase bass absorption and also decrease mid and high frequency absorption. These two things are generally both beneficial in terms of improving sound quality. The membrane can be many things, including thin sheets of wood, mass loaded vinyl, pond liner, cardboard, etc.

I life in an apartment building with wood floors and concrete separating my apartment from my neighbor who recently moved in below me.
She can hear the bass when the stereo is turned up. I’ve raised the speaker six inches off the floor with stands, placed noise canceling spikes with cone coasters and carpet squares under each speaker.
Unfortunately my neighbor’s still complaining.
Any advise would be greatly appreciated. Would love to enjoy my music at high volumes again.

Hi Steven, I don’t have any “easy” suggestions. Either you have to turn your stereo down, or roll off the bass using an EQ of some kind, or give your neighbor earplugs, or only listen when they are out. The alternative is doing extensive retrofit sound isolation work on your and/or her apartment to further reduce sound transmission.

First step is to measure your room to figure out what the issues are. Check out our article on Room Acoustic Measurements for more.

Focus on the resonant peaks at the main listening area. Then find out which locations in the room have the highest sound pressures for the problem frequencies. For example if you measure the room and see peaks at 25Hz, 55Hz, 90Hz, generate a sine wave at each one of those frequencies and use a SPL meter to find the areas of highest SPL. Those are the locations where you want to add bass traps.

I have a square room measuring 12’5″ L, 12’5″ B and 9’5″ H. There is a window with blackout curtains exactly behind and on the right side wall from the setup.

I have 6 zig zag foam bass traps 60x30x30 cm and 12 pyramid absorbers 60x60x5 cm. I tested the room by placing the foam bass traps and sound absorbers as following –

4 absorbers behind the computer/setup
2 absorbers behind the listening position
4 absorbers on the ceiling, above the monitors
1 absorber each on the side wall from the monitors
2 foam bass traps each on left and right side behind the setup touching the ceiling, slighly away from the tri corner as the corner walls behind the setup are curved
2 foam bass traps on the tri corner behind the listening position

The high frequencies sounded crisp and clear but still with some echo. The problem lies with the mid and low frequencies. I can still hear the low end echo. You can clearly hear that the low frequencies are not absorbed properly. I am planning to make custom bass traps using fiberglass or rockwool. Where do you suggest i place the bass traps and how big they should be? Also, if any other suggestion regarding the room acoustics for this particular space would be appreciated.

I’d advise measuring your room to find out what your acoustical issues are. Acoustic measurement equipment is cheap these days, and will really help you pin-point where the issues are. Please take a look at our Room Acoustic Measurement 101 article for more.

Hello, I am going to be using a room in my house for recording and want to soundproof it, the rooms dimensions are 6’10 tall, 136″ long, and 104″ wide.
We are putting pyramid tiles up to absorb the upper range but they are not installed yet. Some of the recording we are going to do will go into the 30 hz range. What are the best bass traps or bass reduction fixes for this size?

Sound isolation and acoustic treatment are two separate things. Acoustic treatment, like “pyramid tiles”, will change the interior acoustics of the room (for the worse I might add, as they will just absorb the high frequencies, leaving the mids and lows untouched). Sound isolation requires mass (e.g. more layers of sheetrock), decoupling (e.g. sound isolation clips) and dampening (e.g. green glue between the layers of sheetrock).

Nyal, thank you for this insightful article and your continued responses to questions 5 years later! I am constructing a pentagonal room, in a diamond shape not with equal angles like The Pentagon. It is a stand-alone structure, and the walls are 7′ high and 42 inches wide.

If you picture the diamond shape, the bottom point, the only 90 degree angle, will be at my back with the door behind me on the right. I will be speaking towards the diamond’s top, toward a flat wall with the 90 degree angle directly behind me. I have two 24″x12″x12″ foam wedge bass traps that I am planning to put along the wall/ceiling corners to my right and left sides. I am doing voiceover work, not singing. Will that placement be effective, even if it isn’t “ideal”?

You will likely have a lot of “room mode” type resonances in that small of a space. You should add as much depth of absorption as possible to all surfaces, and then some wooden slats or perforated plywood to introduce back some mid and high frequency energy.

My room is 11 feet by 11 feet. The ceiling for the east and west walls is 9 feet. From there, it slopes up to the highest point of 11 feet. The flat 11 foot tall portion is about 5 feet wide and runs from north to south along the entire middle of the ceiling. I hope this makes sense.

So basically a cube? You will have your work cut out to deal with the stacking of room mode resonances! I get a lot of questions about where to put bass traps…the basic answer is that you first need to measure to see how bad your issues are, and then figure out where in the room the areas of high SPL are for the problematic frequencies (you can do this using sine wave tones at the problem frequencies and walking around the room with an SPL meter to map the SPL distribution). Once you’ve done that you then need to pick products that will actually work at the problem frequencies. Most commercial products will not do much of anything below 100Hz.

I’m doing a radio room for my church. However, the room that the radio is being moved to has 5 sides. It also leaks outside sound really badly. I’m currently using two 12″x 12″x 24″ bass traps in the two main corners. The plan is to box the room with a 8′ wide curtain with thick fabric which will be behind the announcer. One wall does have a window where I used 2inch thick foam to cover the window to help stop sound. I’m also using 1″x 12″x 12″ tile foam on the walls. With egg carton foam on each side of each bass trap (not sure the dimensions of the egg carton foam). Since I really have no clue what I’m doing what would you suggest using for something like this? Or am I pretty close to being on the right track. The goal is to sound proof the room so nothing goes over the air when live but yet sound great when live. The room that the radio is moving into is right next to the youth room… so we are talking really loud kids to really loud teenagers.

Hi Nathaniel, I’d suggest consulting with a professional to assist you with sound isolating the space and improving the interior acoustics. Many of the companies that sell acoustic treatment and sound isolation products will provide some free design support.

Hello, nice post! I have a doubt. I see there are corner bass traps that are made of stacked triangular shaped rockwool, but if I do a whole wall of staked rockwool, about 60cm deep is it going to be too much or is it going to be more effective or is it a waste of material? Thanks.

60cm is quite deep, I think you’ll want to use a lower density product in that depth. Play around with the calculator at acousticmodelling.com and reference Gearslutz discussions for the gas flow resistivity values (I use 6000 for low density fiberglass bat, 20000 for rigid fiberglass…but rockwool can be double that depending on density). Also note that with a whole wall of absorption you will add a lot of mid and high frequency absorption – you may want to put perforated wood or wood slats over the top of it to prevent over-absorption of mid and high frequencies (room may end up too dead otherwise).

Dear Nyal,
I have to say this is the most informative article I’ve ever come across -along with user questions and your answers- regarding acoustic treatment in general and bass trapping in particular. Thank you for keeping it alive after all these years, wish you a Merry Xmas.
I guess I’ve seen an advice saying that there is no such thing as “too many” bass traps, meaning I can’t go wrong if I even cover more than the 8 corners & 4 wall-wall corners of the room with standerd basstraps i.e. 30*30*50cm. Did I understand that right?
I have a room that is L 3.10m W 3m H 2.80m. I want to acoustically treat that room.
Walls are normal brick / cement, ceiling is normal concrete, ground is normal concrete covered with ceramic, but I have a rug that covers most of it.
I’m planning to use:
4 basstraps on the 4 ground corners.
3 acoustic foam wedge panels 50*50 cm behind the monitors.
2 acoustic foam wedge panels 50*50 cm on the early reflection spots on the right / 2 on the left walls – the level of my ears / listening position.
3 acoustic foam wedge panels 50*50 cm on the ceiling right above the listening position.
2 acoustic foam wedge panels 50*50 cm on the ceiling near the back wall.
3 acoustic foam wedge panels 50*50 cm on the back wall, above the level the 3 panels behind the monitors on my front wall.
I don’t have the luxury for more basstrapss, so I’m thinking I should:
Cover the wall-wall convergence -above the floor basstraps- with 2 acoustic foam wedge panels 50*50 cm one above the other. (I could use 2 extra basstraps on the wall-wall convergence above the floor basstraps of the back wall corners.)
Cover the wall-ceiling convergence around the room with acoustic foam wedge panels 50*50 cm.
Would this setup be good enough for recording / mixing home studio?
What do you recommend I keep, increase, decrease, replace?
I’m sorry for writing this much, had to make the case as clear as possible, thanks in advance.

You are right that it is generally hard to add too many bass traps into a home recording studio, home theater or listening room. However it is definitely possible to add too much broadband absorption (products that absorb over say 500Hz). I would not call foam wedge panels bass traps. If a 4″ fiberglass panel will provide consistent absorption down to 100Hz then a “bass trap” needs to do something more than that. A foam wedge probably does less. If you add too much broadband absorption then your room will end up dead and lifeless in the mid and high frequencies – “over-damped” as some people put it.

You will have some big bass issues in your room because the H, W and L are all very similar to each other (so the room modes “stack – see Room Modes 101). Your wall/ceiling/floor construction are “hard” materials with no flex (unlike a gypsum board / wood stud wall). To get a room like that sounding even remotely neutral in the low end will require a serious amount of bass trapping, likely of the pressure based variety (e.g. metal plate absorbers or VPRs), together with multiple subs and EQ – please have a read of our Bass Optimization eBook if you have not already).